Cresteil Thierry, Monsarrat Bernard, Dubois Joelle, Sonnier Michelle, Alvinerie Paul, Gueritte Françoise
Centre National de la Recherche Scientifique Unité Mixte Recherche 8532, Villejuif, France.
Drug Metab Dispos. 2002 Apr;30(4):438-45. doi: 10.1124/dmd.30.4.438.
Paclitaxel and docetaxel are metabolized by liver microsomal monooxygenases into inactive metabolites further eliminated from the body via the bile route. In spite of their close chemical structure, the two drugs are oxidized by two different enzymes; CYP2C8 catalyzes the 6-hydroxylation on the taxane ring of paclitaxel, whereas CYP3A4 oxidizes docetaxel on the tert-butyl group of the lateral chain in C13. Since paclitaxel and docetaxel differ only by two substitutions, the role of individual modifications was investigated; the regioselectivity of hydroxylation was assessed by high-pressure liquid chromatography/mass spectrometry, and enzymes implicated in individual reactions were identified using human liver microsomes and recombinant P450 expressed in Ad293 cells. The biotransformation of docetaxel, 10-deacetylpaclitaxel, and 10-deacetylbaccatin III was steadily increased (2- to 5-fold) by the addition of an acetyl group in position 10, suggesting that the presence of a hydrophobic group in position 10 stimulated hydroxylation by P450 proteins. The absence of the lateral chain at C13 in baccatin III severely impaired the metabolism supported by CYP3A4. The presence of a tert-butyl group in the lateral chain of docetaxel favored the hydroxylation on the tert-butyl by CYP3A4, whereas the presence of a phenyl group in the lateral chain facilitated the oxidation on the taxane ring by CYP2C8. Collectively, these data strongly suggested that the structure of the lateral chain and the nature of substituent in position 10 play an important role in determining the regioselective oxidation by P450 proteins and modulate the reaction rate by human liver microsomes.
紫杉醇和多西他赛经肝脏微粒体单加氧酶代谢为无活性代谢产物，进而通过胆汁途径从体内清除。尽管它们的化学结构相似，但这两种药物由两种不同的酶氧化；细胞色素P450 2C8（CYP2C8）催化紫杉醇紫杉烷环上的6-羟基化反应，而细胞色素P450 3A4（CYP3A4）氧化多西他赛侧链C13位的叔丁基。由于紫杉醇和多西他赛仅相差两个取代基，因此研究了单个修饰的作用；通过高压液相色谱/质谱法评估羟基化的区域选择性，并使用人肝微粒体和在Ad293细胞中表达的重组P450鉴定参与单个反应的酶。在10位添加乙酰基后，多西他赛、10-去乙酰紫杉醇和10-去乙酰浆果赤霉素III的生物转化稳步增加（2至5倍），这表明10位存在疏水基团可刺激P450蛋白介导的羟基化反应。浆果赤霉素III的C13位没有侧链严重损害了CYP3A4支持的代谢。多西他赛侧链中存在叔丁基有利于CYP3A4对叔丁基的羟基化，而侧链中存在苯基则促进了CYP2C8对紫杉烷环的氧化。总体而言，这些数据有力地表明，侧链结构和10位取代基的性质在决定P450蛋白的区域选择性氧化以及调节人肝微粒体的反应速率方面起着重要作用。
